As one approach to achieve high-speed transmission in a radio communication network system, a multiple-input multiple-output (MIMO) scheme has attracted attention. In the MIMO scheme, a plurality of data signal sequences are transmitted in parallel from a transmitting side having a plurality of antennas to a receiving side having a plurality of antennas, using the same frequency (band).
Further, as another approach to achieve high-speed transmission, there is a multicarrier scheme. In the multicarrier scheme, a plurality of data signal sequences respectively superimposed on a plurality of subcarriers are transmitted in parallel.
In recent years, various studies have been conducted on communication schemes that combine the MIMO scheme and multicarrier scheme. One example is a MIMO-OFDM scheme that combines the orthogonal frequency division multiplexing (OFDM) scheme, which is one example of the multicarrier scheme, with the MIMO scheme (see, for example, Patent Document 1).
In one example of a conventional radio communication network system that adopts the MIMO-OFDM scheme, data signals and pilot signals are time division multiplexed and transmitted. On the receiving side, channel estimation is performed using the received pilot signals. Then, coefficients for demultiplexing a plurality of streams are calculated using a channel estimation value, and the plurality of streams are demultiplexed and demodulated based on that coefficients. Furthermore, the pilot signal is a known signal, and the data signal is not a known signal. That is, the signal sequence of pilot signals transmitted from the transmitting side is known in advance on the receiving side, and the signal sequence of data signals transmitted from the transmitting side is not known in advance on the receiving side.
Patent Document 1: Japanese Patent Application Laid-Open No. 2002-44051